Pumps are the single largest user of electricity in industry in the European Union, and of those pumps, centrifugal pumps represent approximately 73% of all pump types.
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. In a centrifugal pump, the impeller—which typically carries between 4 and 8 vanes—rotates and increases the kinetic energy of the fluid that is being pumped. This kinetic energy is then converted into pressure energy by a stationary volute or diffuser.
The amount of energy given to the fluid is proportional to the velocity at the tip of the impeller. The faster the impeller rotates, then the higher will be the velocity of the fluid at the impeller tip and the greater the energy imparted to the liquid. The kinetic energy of the fluid discharged from the impeller is converted by creating a resistance to the flow. The first resistance is created by the pump volute that catches the fluid and slows it down. In the discharge region, the fluid further decelerates and its velocity is converted to pressure according to Bernoulli's principle. Therefore, the pressure (commonly referred to as ‘head’ when defined in terms of height of fluid) developed is approximately equal to the velocity energy at the periphery of the impeller.
Typically small, (less than 500 gpm capacity), centrifugal pumps are largely inefficient, due principally to the low velocity imparted to the fluid when such pumps are driven by commonly available drive means such as 1725 rpm and 3450 rpm (50 Hz-60 Hz) electric motors.
Like the centrifugal pump, the regenerative pump is a kinetic pump. However the regenerative pump can in many applications offer a more efficient alternative.
In a centrifugal pump, fluid only travels through a centrifugal impeller once. In contrast, in a regenerative pump, fluid travels many times through the vanes of the impeller. A regenerative pump uses an impeller with turbine-type blades mounted on the periphery running in an annular channel surrounding the periphery of the impeller hub. In a known design, the impeller has radial vanes machined into the impeller periphery and the fluid passes through an open annular channel and circulates repeatedly through the impeller vanes.
The suction region of the pump is separated from the discharge region by a barrier on the casing known as a ‘stripper’, creating a hydraulic seal between the high pressure and low pressure sides of the pump. The repeated fluid circulation during the flow process or ‘multistaging’ principally allows regenerative pumps to generate high heads at relatively low specific speeds. In spite of having operating characteristics that mimic a positive displacement pump, (including power directly proportional to head, with maximum power required at shutoff, and a steep head-capacity curve), the regenerative pump is a kinetic pump, i.e. kinetic energy is imparted to the fluid by the series of impulses given to the fluid by the rotating impeller blades. At inlet the fluid splits to both sides of the impeller and continuously circulates between the blades and the channel. When the circulation flow in the impeller and the peripheral flow in the channel unite the momentum exchange that takes places develops a helical or corkscrew fluid motion.
One of the main characteristic of regenerative pumps is the ability to generate high discharge pressures at low flowrates. A regenerative pump typically develops significantly higher heads than a centrifugal pump with comparable impeller size.
The regenerative pump is sometimes also referred to as a peripheral pump, turbulence pump, friction pump, turbine pump, drag pump, side channel pump, traction pump or vortex pump.
In applications requiring high performance, it may be advantageous to connect in series several regenerative pumps to provide a multistage regenerative pump. However, the configuration and efficiency of a multistage regenerative pump is dictated and limited by the manner in which the different units constituting the multistage assembly may be connected to each other. Typically, in a regenerative pump, the inlet and outlet which carry the fluid to and from the impeller region extend radially from an axis of rotation of the impeller. This imparts design and functional limitations on the resulting multistage assembly, not only in terms of configuration and size, but also in terms of performance, as kinetic energy may be lost during transfer of the fluid from the outlet of one pump unit to the inlet of another pump unit.
Therefore, the present invention has identified a need to provide a regenerative pump having improved weight/size ratio and/or performance characteristics, and which is particularly suitable as a multi-stage arrangement.
Examples of applications in which the use of improved regenerative pumps may be of particular significance include Electrical Submersible Pumps (ESPs) for oil recovery, oil pumps for gas turbine engines, and/or oil pumps for turbine gearboxes, e.g. wind turbine gearboxes.
During oil recovery from an oil well, the oil is initially driven to the surface by a number of natural mechanisms. This constitutes the primary recovery stage. These mechanisms include expansion of natural gas near the top of the reservoir, expansion of gas dissolved in the crude oil, gravity drainage within the reservoir and upward displacement of oil by natural water. However, the primary recovery stage typically provides a recovery factor of approximately 5-15% of the original oil.
When the underground pressure becomes insufficient to force the oil to the surface of the oil well, an increase in the recovery factor can be obtained by applying secondary recovery methods. These methods typically include injection of a fluid under pressure such as natural gas or water, or the use of Artificial Lift Systems (ALSs) such as Electrical Submersible Pumps (ESPs) which are inserted at the bottom of the well. The use of secondary recovery techniques typically increases the recovery factor to approximately 15-40%.
Existing ALSs are mainly based on legacy technology which is decades old and which constrains the performance. Conventional ESP arrangements can exceed 20 meters in length in typical hydraulic lift systems. An Artificial Lift System typically contains many components, including a down-hole high speed pump, a high speed motor, a monitoring package and packer; power, communications and hoisting cable; surface power drive and controls; and surface data distribution.
Existing down-hole pumps are, typically, centrifugal devices approximately 3½″ in diameter rotating at approximately 3000 rpm. There is currently limited experience of high speed rotational pump design or relevant testing techniques.
Therefore, the present invention has identified a need for an improved pump for use in electrical submersible pumps, and of such dimensions so as to be capable of being inserted (or replaced) into the oil well without the need for recovering the production tubing.
In an aerospace gas turbine engine, oil pumps are vital to the efficient operation of the engine. Failure of the pumps necessitates a rapid shutdown of the engine. Conventional gas turbine oil pumps are positive displacement type pumps, i.e. they induce a small volume of oil into the inlet port, and transfer it to the outlet port by a rotating mechanism.
Positive displacement oil feed and scavenge pumps are extremely inefficient when the inlet is air-locked. Therefore it is important to ensure that the pump is capable of being primed with oil during engine start-up, and re-primed during any periods of oil interruption (e.g. negative ‘g’ flight manoeuvre, windmill relight). Gas turbine oil system pumps are normally used in recirculatory oil systems, i.e. comprising a combined feed (supply) and scavenge (return) oil loop. Pump elements of such positive displacement pumps are used both as pressure (feed) and scavenge (return) and are incorporated within a common casing. The oil pump pack is driven by an accessory drive system. As the feed oil is distributed to all the lubricated parts of the engine a substantial amount of sealing air mixes with it and increases its volume. Additionally, the bearing chambers operate under differing pressures. Therefore, to prevent flooding, each chamber is typically provided with a scavenge pump. The oil flowing through the feed pump normally has a very low air content, whereas the scavenge pumps have to pump oil which has a high air content. This invariably means that the scavenge pumps are more sensitive to priming problems.
Therefore, the present invention has identified is a need for a regenerative pump, particularly a multiple stage regenerative pump, which is capable of application in a engine oil pump, e.g. a gas turbine engine oil pump or an automotive engine oil pump, and which can be operated in both directions to facilitate a pressure (feed) or scavenge (return) lubrication system.
In a wind turbine, gears typically connect a low-speed turbine blade shaft to a high-speed generator shaft. Rotational speeds increase typically from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm which are required by most generators to produce electricity. This power transfer is conventionally carried out through the use of gearbox. The gearbox is an onerous and heavy part of the wind turbine which requires lubrication. Typically, lubrication is performed using positive displacement oil pumps similar to the oil pumps used in gas turbine engine oil systems.
Therefore, the present invention has identified is a need for a regenerative pump, particularly a multiple stage regenerative pump, which is capable of application in a gearbox oil system, e.g. a wind turbine gearbox oil system, and which can be operated in both directions to facilitate a pressure (feed) or scavenge (return) lubrication system.
Fuel pumps for use in, e.g. automotive engines, can be of various designs. There is a need for a pump suitable for use in fuel pumps, e.g. in automotive engine fuel pumps, having improved weight/size ratio and/or performance characteristics.
Process manufacturing for, e.g. the pharmaceutical industries, typically involves pumping fluid(s) reacting in or produced by the pharmaceutical process. Similarly, process manufacturing in, e.g. the petrochemical industry, typically involves pumping petrochemical substances, e.g. reacting in or produced by a petrochemical process. There is a need for a pump suitable for use in process manufacturing, having improved weight/size ratio and/or performance characteristics.
Water pumps, e.g. for use in fire engines or water tenders, typically require high performance pumps capable of delivering large water output under high pressure. There is a need for a pump suitable for use in high performance water pumps such as water pumps used in fire engines, having improved weight/size ratio and/or performance characteristics.
It is an object of at least one embodiment of at least one aspect of the present invention to obviate and/or mitigate one or more disadvantages in the prior art.
It is an object of at least one embodiment of at least one aspect of the present invention to provide a regenerative pump having improved weight/size ratio and/or performance characteristics.
It is an object of at least one embodiment of at least one aspect of the present invention to provide a multistage regenerative pump having optimised weight/size ratio and/or performance characteristics.
It is an object of at least one embodiment of at least one aspect of the present invention to provide an improved impeller for use in a velocity pump, e.g. a multistage regenerative pump.
It is an object of at least one embodiment of at least one aspect of the present invention to provide a casing for use in a velocity pump, e.g. a multistage regenerative pump.